Evolution and diversity of reptiles driven by 60 million years of climate change

Artistic reconstruction of reptile adaptive radiation in an Earth ecosystem during the hottest time in Earth’s history. The image depicts a massive, large-headed carnivorous erythrosuchid (a close relative of crocodiles and dinosaurs) and a tiny gliding reptile about 240 million years ago. The erythrosuchid pursues the gliding reptile and propels itself using a fossilized skull of the extinct Dimetrodon (ancestor of the first mammals) in a hot and dry river valley. Credit: Henry Sharpe

Reptiles had one hell of a coming out party just over 250 million years ago, at the end of the Permian period and the beginning of the[{” attribute=””>Triassic.

Their rates of evolution and diversity began exploding, leading to a dizzying variety of abilities, body plans, and traits. This helped to firmly establish both their extinct lineages and those that still exist today as one of the most successful and diverse animal groups the world has ever seen. For the longest time, scientists explained this flourish by reptile competition being wiped out by two of the biggest mass extinction events in the history of the planet. These occurred around 261 and 252 million years ago.

This explanation has been rewritten by a new Harvard-led study that reconstructed how the bodies of ancient reptiles changed and compared it to the effects of millions of years of climate change.

Harvard paleontologist Stephanie Pierce’s lab shows that the morphological evolution and diversification seen in early reptiles started years before these mass extinction events. Moreover, they were directly driven by what caused the mass extinction events in the first place — rising global temperatures due to climate change.

“We are suggesting that we have two major factors at play — not just this open ecological opportunity that has always been thought by several scientists — but also something that nobody had previously come up with, which is that climate change actually directly triggered the adaptive response of reptiles to help build this vast array of new body plans and the explosion of groups that we see in the Triassic,” said Tiago R. Simões, lead author on the study and a postdoctoral fellow in the Pierce lab.

“Basically, [rising global temperatures] triggered all these different morphological experiments — some that worked quite well and survived for millions of years to this day, and others that all but disappeared a few million years later,” Simões added.

In the article, which was recently published in the journal Scientists progressthe researchers expose the vast anatomical changes that took place in many groups of reptiles, including the precursors to crocodiles and dinosaurs, in direct response to major climate changes concentrated between 260 and 230 million years ago.

The study takes a close look at how a large group of organisms are changing due to climate change, which is particularly relevant today as global temperatures continually rise. In fact, the rate of carbon dioxide released into the atmosphere today is about nine times greater than it was during the period that culminated in the greatest mass extinction due to climate change of all. time 252 million years ago: the Permian-Triassic mass extinction.

“Major changes in global temperature can have dramatic and variable impacts on biodiversity,” said Stephanie E. Pierce. She is the Thomas D. Cabot Associate Professor of Organismal and Evolutionary Biology and Curator of Vertebrate Palaeontology at the Museum of Comparative Zoology. “We show here that rising temperatures during the Permian-Triassic led to the extinction of many animals, including many mammalian ancestors, but also triggered the explosive evolution of others, especially reptiles that dominated the Triassic period.”

The study involved almost eight years of data collection and required a heavy dose of camera, CT scans and tons of passport stamps as Simões traveled to over 20 countries and over 50 different museums to take scans. and snapshots of over 1,000 reptilian fossils. .

With all the information, the scientists created a large dataset which was analyzed with state-of-the-art statistical methods to build a diagram called an evolutionary time tree. Time trees reveal how closely the earliest reptiles were related to each other, when their lineages first appeared, and how quickly they evolved. Then they combined it with global temperature data from millions of years ago.

The diversification of reptile body plans began about 30 million years before the Permian-Triassic extinction event, making it evident that these changes were not event-triggered as previously thought. Although the Extinction events helped kick them into high gear.

The dataset also showed that the increase in global temperatures, which began around 270 million years ago and lasted until at least 240 million years ago, was followed by changes fast bodily in most reptile lineages. For example, some of the larger cold-blooded animals have evolved to become smaller so that they can cool themselves more easily; others have evolved to live in water for the same effect. This latter group included some of the most bizarre forms of reptiles that were about to go extinct, including a tiny chameleon-like creature with a bird’s skull and beak, a giant, long-necked marine reptile once believed to be Loch Ness. monster, and a hovering gecko-like reptile with wings. It also includes the ancestors of reptiles that still exist today such as turtles and crocodiles.

The small reptiles, which gave rise to the first lizards and tuataras, followed a different path than their larger reptile brothers. Their rates of evolution have slowed and stabilized in response to rising temperatures. Investigators believe this is because small reptiles were already better adapted to the increasing heat since they can more easily shed heat from their bodies compared to larger reptiles when temperatures rose very quickly all around. Earth.

The scientists say they plan to extend this work by studying the impact of environmental disasters on the evolution of organisms with abundant modern diversity, such as major groups of lizards and snakes.

For more on this research, see Researchers Discover Global Warming Spawned the Age of Reptiles.

Reference: “The successive climatic crises in the deep past led to the early evolution and radiation of reptiles” by Tiago R. Simões, Christian F. Kammerer, Michael W. Caldwell and Stephanie E. Pierce, August 19, 2022, Scientists progress.
DOI: 10.1126/sciadv.abq1898

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